The goals of these studies are: (1) to identify and localize the transcriptional regulatory sequences within the long terminal repeats (LTRs) of different gibbon ape leukemia virus (GALV) strains; (2) to compare the relative transcriptional ability of the different strains and examine their tissue specificity of expression; and (3) having identified the regulatory sequences, to isolate and purify the trans-acting cellular factors which interact with these sequences to enhance the transcriptional activity.